The present invention relates to a surface-coated optical fiber or, more particularly, to an optical fiber of fused quartz glass used in the optical communication technology having a protective coating layer formed of a novel coating composition.
Although several different materials are proposed for optical fibers used in the optical communication technology including fused quartz glass, multi-component glass, plastic resins and the like, quartz glass-made optical fibers are primarily employed in view of the advantages of these fibers such as their light weight, low transmission loss, non-inductiveness, heat resistance, weathering resistance, high transmission capacity and the like. Such quartz glass-made optical fibers are typically provided with a surface coating layer to avoid possible damages on the surface by the use of various kinds of coating materials.
The coating composition used for the surface coating on quartz glass-made optical fibers should satisfy several requirements. For example, the coating layer formed of the coating composition should be usable over a wide temperature range without being affected by the changes in temperature and should be effective for the reinforcement and stress relaxation of the optical fibers. Further, the coating layer should be free from the problems of increased transmission loss due to microbending and noise generation due to light scattering. A coating material of the type preferred in these respects is a composition comprising a silicone, i.e. an organopolysiloxane resin. Organopolysiloxanes are advantageous as a coating material on quartz glass-made optical fibers in that these organopolysiloxanes exhibit good adhesion to the substrate surface with inherent affinity to vitreous materials by virtue of their chemical structure and excellent workability in the coating. This is due to the fact that the viscosity of these materials does not change significantly with temperature change. On the other hand, the organopolysiloxanes are defective in that coating films made of these materials exhibit relatively poor mechanical properties in so that the coating layer is sometimes broken or peeled from the substrate surface in the course of the application or in the subsequent post-treatment.
On the other hand, other types of coating materials practically used on quartz glass-made optical fibers include urethane acrylate, epoxy acrylate, polybutadiene acrylate and the like. These organic resins are, however, not quite satisfactory and have disadvantages such as low affinity to the surface of vitreous materials, difficulty in obtaining a viscosity suitable for the coating application and the temperature must be strictly controlled in the coating application because the viscosity of these materials are greatly dependent upon temperature.